Fly ash as Pozzolana

 

Pozzolana

 

Fly ash has certain reactive minerals such as soluble silica that can react with lime in the presence of water at normal temperature to form calcium silicate hydrate as binding mineral. It does not only produce higher quantity of binder, but fills the pores due to availability of more fine non reactive particles .

The importance of certain properties such as fineness and loss on ignition can explained from Table 2.

 

Fly ash in cement mortar

 

If fly ash is added in cement mortar for brickwork and plaster, it not only improves long age strength of mortars but also makes mortar very cohesive and workable (Table 3). There is overall saving of 5 % of OPC and to a certain extent sand with the use of fly ash (2).

 

Fly ash in plain concrete mixes

 

Nominal mixes for plain concrete (Table 4) were designed with flyash obtained from PSEB Roper for their use (3). The percentage of fly ash used will be about 100 to 150% of cement used in these concretes. The basic advantage is ease of compactability of such mixes with vibrator with extra strength.

 

Fly ash in RCC structures

 

Recent construction in India

 

Concrete mix designs were done for M 20 grade concrete mixes with and without flyash for workability of 50 mm slump using a superplasticizer to obtain target strength at 28 days. 43 grade cement and flyash (4) were used for this purpose along with crushed stone quartzite aggregates and sand conforming to requirement of IS: 383-1970(5). Details of mixes are given in Table 5.

The properties of concrete such as compressive strength at 7, 28 days, pH values, drying shrinkages as per IS 1199-1959 (6) water permeability as per IS 3085-1965 (7) and resistivity to chloride ions in terms of current passed in coulombs per six hours was determined as per ASTM C-1202-94 (8).

The built environ

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